At T-Mobile, get up to $650 per line toward Early Termination Fees when you trade in your current carrier's phone and switch to T-Mobile. (That's up to $300 trade-in per phone, plus up to an extra $350 based on the Early Termination Fees on your final bill.) That's the best such credit offer we've seen for switching to this service. Plus, several coupons are available to drop up to $48 off select T-Mobile phones: